I have a minor umbilical hernia. Which types of exercise are advised and which should be avoided?

I am a 24 year-old male, with a lean build and a relatively active lifestyle (3-4 hours of exercise per week). Recently, my doctor, a surgeon, informed me that I have a small "umbilical hernia," which is not large enough to warrant surgery. Despite my diagnosis, I would like to remain physically active. Apart from yoga, I am not sure what kind of physical activity is acceptable.